The proposed research aims towards a better understanding of the role of calcium in the activation of contraction in striated muscle. Experiments are proposed to: (1) measure the mechanical properties of skinned muscle fibers during the rise and fall of activation, (2) study the effects of various mechanical perturbations on the level of activation, and (3) develop more direct methods for the detection of activation in this preparation. To do this, a system will be developed to measure optical absorbance or fluorescence simultaneously with mechanical activation of skinned fibers. The results of these experiments are expected to lend insight into the relationship between the mechanical and biochemical properties of striated muscle, and to learn about the interaction between mechanical behavior and activation. They will contribute, therefore, to the understanding of the molecular mechanisms involved in the physiology of muscle (skeletal and cardiac) contraction. The knowledge obtained from this research will be relevant and important in cardiology and skeletal muscle pathology.